1. Field of the Invention
The present invention is generally related to lithography systems, and more particularly, to polarization of light in a lithography system.
2. Background Art
Lithography is a process used to create features on a surface of a substrate. The substrate can include those used in the manufacture of flat panel displays, circuit boards, various integrated circuits, print heads, micro/nano fluidic devices and the like. A semiconductor wafer, for example, can be used as a substrate to fabricate an integrated circuit.
In an exemplary lithography process, an image, often formed on a reticle, is used to transfer a desired pattern onto a substrate. During lithography, a wafer, which is disposed on a wafer stage, is exposed to an image projected onto the surface of the wafer corresponding to the desired image pattern.
The projected image produces changes in the characteristics of a layer, for example a resist layer, deposited on the surface of the wafer. These changes correspond to the features projected onto the wafer during exposure. Subsequent to exposure, the layer can be etched to produce a patterned layer. The pattern corresponds to those features projected onto the wafer during exposure. This patterned layer is then used to remove or otherwise process exposed portions of underlying structural layers within the wafer, such as conductive, semiconductive, or insulating layers. This process is then repeated, together with other steps, until the desired features have been formed on the surface of the wafer.
Lithographic processes are used to produce increasingly complex devices at an increased level of miniaturization. Lithography systems can be described in terms of their numerical aperture (NA) and the NA of systems is increased to facilitate production of more densely populated devices. In very high NA lithography, the capacity of the process will be limited by the available level of imaging accuracy. Systems that can project an image with higher optical efficiency and higher contrast levels can produce more highly integrated devices in high-NA lithography.
Thus, there is a need for an improved apparatus and method for increasing optical efficiency and contrast levels in a lithography system.